This invention pertains generally to frequency multipliers and more particularly to a frequency doubler and a frequency tripler.
As is known in the art, frequency multipliers are used to derive from an input signal having an input frequency an output signal having an output frequency greater than the input frequency of the input signal. Typically, the output frequency is an exact integral multiplier of the input frequency. For example, a frequency doubler provides an output signal with a frequency that is twice the frequency of the input signal and a frequency tripler provides an output signal with a frequency that is three times the frequency of the input signal. With a combination of frequency doublers and frequency triplers, a signal with a desired frequency can be provided from a signal having a much lower frequency.
A critical characteristic of a frequency multiplier for many applications is that the frequency multiplier must provide an output signal with little phase noise added to the input signal. Phase noise is used to describe the the input signal. Phase noise is used to describe the characteristic randomness of short-term frequency fluctuations and is an important indicator of a given signal generator,s short-term frequency stability. In a signal generator application, each element of the signal generator including the frequency multiplier must have a low phase noise characteristic so that the output signal of the signal generator will have little phase noise. It is also desirable for the frequency multiplier to provide a output signal with a controlled output signal level with little variation to minimize variations introduced by a signal provided by the signal generator circuitry. Thus it is desirable to provide a frequency doubler and a frequency tripler that provides an output signal with little phase noise added to an input signal fed thereto, the output signal further having a constant signal level.